Bony bridging of the mylohyoid groove of the human mandible

Bony bridging of the mylohyoid groove of the mandible (mylohyoid bridging) is one of the minor cranial variants and its frequencies in human groups have been used for population studies. Its value as a genetic marker, however, has not yet been established. Formalin-fixed human lower jaws of 16 individuals and human mandibles of 2,158 individuals were morphologically and statistically examined. The findings indicate that the two basic types of mylohyoid bridging, lingular type and bridge type, can be treated as one and the same trait. Bilaterality in the expression and the occurrence independent of age and sex are consistent with the assumption that genetic background is relevant to its formation. Moreover, relationships of human groups based on the frequency of mylohyoid bridging are compatible with those based on dental morphology and human genetic analysis. Although the mylohyoid bridging occurs with high frequency in Neanderthals, it can also be observed in European Upper Palaeolithic humans with distinctly higher frequency than in subsequent populations. This finding appears to be important in arguments regarding the population history in Europe, if genetic background is relevant to the expression of mylohyoid bridging as assumed from the present study.